Electrical safety in the laboratory

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Electrical safety in the laboratory

• CHM 605, 2007

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This lecture is mostly for typical labs, users
of equipment

• The typical laboratory contains a wide variety of
  electrically-powered equipment including
  stirrers, shakers, pumps, hot plates, heaters,
  power supplies, ovens, and electrophoresis
  equipment.

• Atypical laboratories and users need to learn
  more, see Dr. Santini and/or his lecture notes.

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Hazards, risks of

• electric shock (which btw can cause death)
• due to completing a circuit.
• fires
• due to poorly installed or maintained systems.
• due to sparks serving as an ignition source for
  flammable or combustible materials.

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How to protect yourself?

• Understand some basic principles, guidelines.
• Do NOT just use your "common sense.

Common sense
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Basic principles

• A little advanced background
• Being prepared
• Receptacle safety
• Power supply safety
• Power cord safety
• Circuit protection and human protection
• Flammable materials
• General electrical safety

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Some background (1/5)
(These are externally measured currents! Thirty
micro-amps in the heart is lethal.)

• More than 3 ma
• painful shock
• More than 10 ma
• muscle contraction no-let-go danger
• More than 30 ma
• lung paralysis- usually temporary
• More than 50 ma
• possible ventricular fib. (heart dysfunction,
  usually fatal)
• 100 ma to 4 amps
• certain ventricular fibrillation, fatal
• Over 4 amps
• heart paralysis severe burns. Usually caused by
  gt600 volts

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Some background (2/5)

• AC, DC or ACDC voltages above /-30 volts peak
  value are potentially a risk
• Because current can flow through an internal path
  in the human body that includes the heart and or
  the chest muscles that control breathing.
• Usually, the overall circuit includes
  unpredictable parallel paths on the skin that
  reduce the risk.

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Some background (3/5)

• The most likely source of exposure in the lab
  environment is to line power at plugs,
  receptacles and inside equipment.
• Typical line voltage values are 120, 208 and 240
  VAC.
• DC power sources range from 5 VDC to over 1000
  VDC. (Whole nother lecture.)

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Some background (4/5)

• Most common electrical shock accident factors
• User is careless or circumvents safety devices
  and makes physical contact with high voltage.
• User creates unsafe condition that is not
  immediately obvious, such as a shock hazard or
  thermal run-away condition.

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Some background (5/5)
Single Phase AC Waveform
Nominally, a sinusoid with an effective value
of 120 VAC.
60 Hz rate (50 Hz)
Electrical components must withstand the peak
voltage! DC to AC converters do not produce
sinusoidal output unless specified clearly to
have this capability.
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Being prepared (1/3)

• Electrical panels should be locked and not used
  as emergency shut-offs.
• If you need an emergency shut-off, request an
  installation.
• Leave at least a 3-foot clearance around
  electrical panels for access by maintenance
  personnel.

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Being prepared (2/3)

• Plan ahead for what steps will be taken in the
  event of a power loss.
• Think about potential vapor/gas release from
  vapor-generating processes or chemical fume
  hoods if power is lost.

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Being prepared (3/3)

• Conduct a periodic inspection of laboratory
  electrical equipment to be sure it is in good
  condition.
• Remove equipment from service if in poor
  condition and replace or have it repaired by a
  qualified repair person

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Outlet Receptacles

• Electrical outlets should have a grounding
  connection and accept three-prong plugs.
• Multiple plug outlet adapters are not allowed
  unless 15 amp fused and UL approved.
• Power strips must be 15 amp fused and UL approved.

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Power Cords

• Power cords must have grounding plugs or be
  double insulated.
• Inspect power cords -- no damage, no fraying.
• Place cords carefully avoid water, chemicals
• Avoid dangling cords and cords at floor.
• Take care to not smash or walk on cords.
• Keep cords away from hot surfaces.
• Never pull on or hang something by the power cord.

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Power Cords photo

• Avoid dangling cords and cords at floor.

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Power supplies

• Portable power supplies are common, are extremely
  high energy sources, must be used carefully.
  Never attach an exposed connector (such as an
  alligator clip) to a power supply.
• Extension cords are not allowed. Electrical
  power strips surge suppressors (max 15 a fused,
  UL listed) are.

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Circuit protection (1/2)

• Not more than two high current devices (e.g.
  oven, centrifuge, microwave) are to be plugged
  into the same outlet.
• Fuses and circuit breakers protect equipment,
  prevent fires. Not people.

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Circuit protection (2/2)

• Ground-fault circuit interrupters (GFCI) protect
  people -- disconnect current almost instantly to
  protect when large current detected. GFCI outlets
  or portable GFCIs are used near sinks and
  potentially wet locations.
• Keep electrical equipment (and yourself while
  using it) away from water unless its rated for
  wet use.

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Flammable materials
(electricity)

• Keep flammable materials away from electrical
  equipment.
• Receptacles providing power for equipment used
  inside a fume hood should be located outside the
  hood. Including power strips!
• Most equipment IN YOUR HOUSE AND IN YOUR LAB, is
  not non-sparking even though it would be nice.
• Refrigeration flammable materials may only be
  stored in lab safe or explosion proof
  refrigeration/freezing units. These have the
  obvious sources of ignition removed.
• Know when you must plug equipment into a variable
  power transformer rather than directly into a
  receptacle
• Oven drying of organic materials has lead to
  explosions caused by electrical ignition.

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Sparking appliances

• Most equipment IN YOUR HOUSE AND IN YOUR LAB, is
  not non-sparking even though it would be nice.

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General Electrical Safety

• Avoid contact with energized electrical circuits.
  
• Only qualified electrical workers may install,
  service or repair electrical equipment.